1. Field of the Invention
This invention relates to an axle and suspension assembly for mounting two unsteerable wheels of a motor vehicle, wherein a crosspiece is provided with elastic mounting bodies, which are adapted to be secured to a body or another rigid structure of the motor vehicle, and two wheel carriers, which are linked to said crosspiece and constrained to move in a generally vertical direction, each of said mounting bodies has different stiffnesses in different directions in a generally horizontal plane, and all hinges of the assembly are provided with elastic liners.
2. Description of the Prior Art
An axle and suspension assembly of that kind has been disclosed in Published German Application No. 2,319,943. In that known assembly the wheel carriers are linked to the rear side of the crosspiece by means of rigid lower wishbones, which extend outwardly and downwardly from the crosspiece, and the wheel carriers are connected to the body or another rigid structure of the vehicle by means of spring elements constraining the wheel carriers to move in a generally vertical direction. Under the action of the lateral forces exerted when the vehicle is cornering the crosspiece can assume an oblique position so that a toe-in or toe-out action will be exerted on the wheels and a certain self-steering action will be obtained. But that oblique position of the crosspiece will depend only on the instantaneous characteristics of the two mounting bodies, and said characteristics will be determined by the different stiffnesses of said mounting bodies in different directions. For this reasons the mounting bodies must not be too soft because this would impair the riding comfort. The fact that the self-steering action depends only on the elastic mounting bodies has also the disadvantage that the crosspiece will also assume an oblique position and a toe-in or toe-out action will also be obtained when different frictional forces act between the road and the two wheels carried by the axle or in the case of a sudden change from braking to acceleration or vice versa although in such cases an oblique positioning of the crosspiece will be undesirable and will adversely affect the safety of the traveling vehicle. If the mounting bodies are too soft, the inertial forces of the entire axle and suspension assembly cannot perfectly be controlled in case of sudden steering actions of the driver and the self-steering action of the axle and of the unsteerable wheels will be undesirably delayed.
It is also known to link each wheel carrier to the crosspiece by two lower transverse control arms and to connect each wheel carrier to the body or another rigid structure of the vehicle, by means of a longitudinal control arm and a spring strut in an arrangement in which the longitudinal axes of the lower transverse control arms intersect at a point which is disposed on the outside of the adjacent wheel and axially spaced therefrom. Such an arrangement has been dislcosed by Jornsen Reimpell in Fahrwerktechnik 1, VOGEL-Verlag, 5th edition 1982, page 402). But in that known arrangement the crosspiece is rigidly secured to the body or another rigid structure of the vehicle so that only a small toe-in or toe-out effect can be achieved because such effect is allowed for only by the relatively small volume of elastic material which consists of the elastic liners of the hinges. If larger volumes or a softer elastic material were used for such liners, the directional control of the wheels will be adversely affected, particularly because all braking and accelerating forces must be transmitted to the body or other rigid structure of the vehicle by means of the elastic liners.
Published German Application No. 1,911,795 discloses a rigid axle, which by a centrally disposed, elastic mounting body is secured to the body or another rigid structure of the vehicle and is also connected to said body or rigid structure by two diagonal struts. In that known arrangement, the axes of the diagonal struts intersect at a point which is disposed on the vertical longitudinal center plane of the vehicle at the rear of the rigid axle. That design has the disadvantage that the toe-in or toe-out effect is restricted by the limitation of the pivotal movement of the rigid axle and the self-steering behavior cannot be influenced in another way. The range of movement is limited by the centrally disposed, elastic mounting body so that the range in which the material and design of the mounting body can be selected to improve the riding comfort will also be restricted. An excessively soft elastic material will also involve the disadvantages which have been stated hereinbefore in connection with the arrangement comprising a crosspiece and rigid lower wishbones. Similar remarks are applicable to another known wheel suspension, which is known from Published German Application No. 2,818,198 and in which the lower transverse control arms are directly pivoted to the body or another rigid structure of the vehicle and a diagonal control arm provided with elastic hinges is associated with each wheel carrier.